The human eye functions to provide vision by transmitting light through a clear outer portion called the cornea, and focusing the image by way of a lens onto a retina. The quality of the focused image depends on many factors including the size and shape of the eye, and the transparency of the cornea and lens. When age or disease causes the lens to become less transparent, vision deteriorates because of the diminished light that can be transmitted to the retina. This deficiency is medically known as a cataract. An accepted treatment for cataracts is to surgically remove the cataract and replace the diseased lens with an artificial intraocular lens (IOL). In the United States, most cataractous lenses are removed using a surgical technique called phacoemulsification. During this procedure, a thin cutting tip or needle is inserted into the diseased lens and vibrated ultrasonically. The vibrating cutting tip liquefies or emulsifies the lens, which is aspirated out of the eye. The diseased lens, once removed, is replaced by an IOL.
More recently, water-jet based liquefaction devices that generate pulses of heated surgical solution have been introduced for cataract surgery and other ophthalmic procedures and treatments. Liquefaction handpieces heat a balanced salt solution, and the heated solution removes the cataractous lens. For example, FIG. 1 generally illustrates an AquaLase® handpiece, available from Alcon Laboratories, Forth Worth, Tex. The device or handpiece assembly 10 (generally “handpiece”) shown in FIG. 1 includes a body 11, such as a titanium handpiece body, a tip 12, such as a polymer tip, an irrigation sleeve 13, an aspiration line 14, a solution line 15, e.g., for a balanced salt solution, and an irrigation line 16.
The tip 12 is disposed at the end of the handpiece 10. The irrigation sleeve 12, is placed over the tip 12 to provide an environment for irrigation solution to be delivered to the eye via the irrigation line 16. The aspiration line 14 carries fluid that is drawn from the eye by a vacuum, and the solution line 15 delivers a heated balanced salt solution, which breaks apart the cataract. Irrigation fluid is delivered through the irrigation line 16 and flushes cataractous material that is removed or broken by the balanced salt solution.
Referring to FIGS. 2A and 2B, in use, the distal end of the tip 12 is placed within a cataract 20 in an eye 21 and propels pulses of heated solution 22 through the tip 12 and at the cataract 20. Each pulse 22 can include about four microliters of solution 22. The solution 22 is heated by heating elements 23 within the handpiece 10 as the solution 22 passes between the elements 23 and through the handpiece body 11. The amount of energy 24 provided to the handpiece 10 is a factor that controls the temperature of the heating elements 23 and the heating of the solution 22. The pulses of warmed solution 22 impact the cataract 20, resulting in liquefaction, during which the cataract 20 is eroded or dissolved. Cataract material 20 can then be washed and aspirated from the eye 21.
Liquefaction handpieces provide a number of advantages over other surgical systems and handpieces. For example, since liquefaction handpieces do not involve ultrasonic motion, they facilitate a watertight incision in the eye and provide various safety advantages, including reduced risk of capsule rupture and reduced eye turbulence. Liquefaction handpieces also typically operate at lower temperatures compared to other handpieces (since they do not have any moving parts), thus reducing thermal stress to the eye. Liquefaction handpieces can also be easier for a surgeon to control and manipulate. While liquefaction has been successfully used and provides various benefits and alternative surgical solutions, the manner in which energy is delivered to the liquefaction handpiece can be improved to provide improved control over the solution pulses delivered to the cataract.
Referring to FIGS. 3 and 4, one known liquefaction handpiece includes a mechanism that is responsible for controlling the operation and the handpiece and control parameters. The mechanism includes an amplifier or engine 30 that produces “High-Voltage” (HV) energy 31. FIG. 4 illustrates HV energy as a continuous series of pulses 31. A gating mechanism or other suitable component 32 generates a series of control or RF Enable pulses (RFEN) 33. The control pulses 33 define an active period 34 and an inactive period 35. The active period 34 serves as a gate to pass pulses 31 from the HV engine 30, whereas pulses 31 are not provided as an output during the inactive period 35, resulting in a series of HV pulses 33 that are provided to the liquefaction handpiece device 10.
It is important to control, maintain, and monitor the amount of HV energy that is generate by the engine 30 and applied and utilized by the handpiece 10 for optimum handpiece 10 operation. Theoretical handpiece operation is based on a constant voltage source, the output of which is provided to a capacitor that is charged and periodically discharged to provide energy to the handpiece in a series of controlled pulses. Referring to FIG. 5, HV energy, therefore, is required to be present only for those instances where the energy is applied to the handpiece using the RFEN pulses 33 during a burst signal or window 50. The combination of software and hardware support provides a virtual constant voltage for the handpiece.
With the controls shown in FIGS. 3-5, capacitors must be fully charged by the time a control pulse triggers discharge of a capacitor to provide stored energy to the handpiece. Known systems typically charge capacitors as quickly as possible to ensure that the capacitors are sufficiently charged or provide a constant voltage source through a transformer, which can be large and bulky, e.g., about 12″×12″. Further, capacitors are charged as quickly as possible since the circuit can be easily implemented by pre-setting the charge rate. As a result, however, at the beginning of a capacitor recharge cycle, charging the capacitor as quickly as possible results in a current spike, which can complicate circuit design and reduce circuit performance and place unnecessary burdens on the system power source.
While known control and recharging systems has been used effectively in the past to drive liquefaction handpieces, they can be improved by using feedback to adjust and adapt operating parameters that are suitable for different handpieces and handpiece components. Systems should also be able to adapt to different components and their operation rather than relying on preset operating parameters that cannot be adjusted. Further, known systems can be improved by allowing for system adjustments that more accurately reflect actual operation of system components. Systems should also be more efficient by reducing or eliminating current spikes in favor of more gradual current transitions. Embodiments of the invention fulfill these unmet needs.